No. XI. 



Conchologieal Observations <m Lamarck's Fai/ii/i/ of Naiades. 

 By Philip Hoidbrooke Nicklin. Read 6 March, 1829. 



THE genus Unio, and its congeners, have become objects 

 of great interest to naturalists in all parts of the world. 

 American conchologists seem to have had their attention par- 

 ticularly drawn to these objects by the immense number and 

 almost infinite varieties of them that arc nourished by the 

 great rivers of the West and their tributaries. Many beauti- 

 ful species of Unio and Ana don t a have been added to La- 

 marck's family of Naiades, by the useful labours of Messrs 

 Say. Barnes, Green, and Isaac Lea; and the former of these 

 naturalists hasthoughl il necessary (oadd a new genus, called 

 Jdlasmodonta*, to the same family. 



DoubN have been expressed by several distinguished con- 

 chologists. whether the family of Naiades contains more than 

 one genus, or at most two. The new genus Jllasmodonta of 

 Mr Say seems to form a link of close connection between 

 . biodonta and Unio; and the three genera exhibit such va- 

 rious forms of hinge, that, in many instances, it is difficult to 

 determine to which genus the individual should be referred. 

 Mr Isaac Lea has upwards of forty varieties of Unio cornufus; 

 which, if arranged in a particular order, exhibit so gradual a 



* I'rom a priv., \>.a.efjii lamina, and iJevt dent; meaning without llic lamellar tooth. 



\ on. 1 1 f . — 5 ii 



